piston scoring advice

[blrobison]

I just purchased a used Husqvarna385xp and pulled off the muffler to discover some mild scoring on the piston. The rings look slightly marked but compression is still around 140 so I'm not greatly concerned. The cylinder looks spotless though.

What I'm curious is if there is an easy treatment or process to help repair or slow the scoring? (other than using full synthetic fuel oil mix) I'd like to avoid ripping the top end off since the scoring isn't that extreme, but I know that if left untreated, it will get worse. Thanks in advance.

 

[sld961]

Pics would be helpful. There is a reason it scored. If it was tuned improperly it out could be fixed with a good tune. If you have an air leak, it will get worse. If there is any aluminum transfer, it will get worse. Again, pics would help us determine how "minor" it is.

 

[blrobison]

I'll get some on later tonight

 

[nmurph]

DO NOT CONTINUE TO RUN IT. You need to determine the cause of the scoring or it will get worse and you may end up with a cylinder that is not useable. You have already lost a good bit of compression (should be around 165psi). The scoring might be from incorrect needle settings, air leaks around the seals, base gasket, loose carb. One common problem with 385's that is sometimes hard to locate is that they leak around the inner race of the PTO side bearing, between the crank and race. If that is the source of the air leak there is nothing to do but to split the saw and replace it with the updated bearing.

 

[blrobison]

The previous owner had been using it for milling so I'm guessing that at some point he overheated it and that's what started the scoring. I'll check for air leaks, but I'm pretty sure that the milling did it in. I should have pictures tonight. Also recheck the compression since the previous reading was on a cold engine.

 

[nmurph]

A cold engine is the correct way to check compression.

 

[blrobison]

Wouldn't a warm engine allow the piston and rings to expand which would increase compression?

 

[nmurph]

No, it will read higher when cold and gives a better baseline.

 

[blrobison]

I redid the compression test and got 150psi. Here's some pics of the cylinder and piston:

 

[o8f150]

if it was me,,, which means nothing,,, I would get a meteor piston and caber rings and put in it,, the scoring isn't severe but it will get worst,, so do it now so you know for sure the cylinder is savable

 

[Marshy]

Its highly likely that your cylinder wall look similar to the piston above the exhaust port. Take 30 minutes and pull the top end and inspect it. It might change your mind about continuing to run it.

 

[blsnelling]

I would pull the jug and polish both the piston and cylinder wall.

 

[blrobison]

I pulled the cylinder off and the exhaust port did have some grooves. Doesn't seem too deep so I'm going to get some muriatic acid and fine sandpaper to hone them out. Any advice for this process? (I've never had to do a top end repair)

 

[sld961]

Watch this video.

http://www.arboristsite.com/community/threads/how-to-remove-aluminum-transfer-without-acid.248325/

 

[mdavlee]

Meteor pistons come with caber rings. Sometimes you get f cast and sometimes you don't.

 

[turtle561]

how can you tell if they are the f cast rings ? i just did a meteor piston and rings in my 028. they looked silver.
be sure to clean the ring grooves and check the backs of the ring for carbon build up. this pushes ring out.